I. Field of the Invention
The present invention relates generally to antennas. More specifically, the present invention relates to a circularly polarized dielectric resonator antenna. Still more particularly, the present invention relates to a low profile dielectric resonator antenna for use with satellite or cellular telephone communication systems.
II. Description of the Related Art
Recent advances in mobile and fixed wireless phones, such as for use in satellite or cellular communications systems, have renewed interest in antennas suitable for such systems. Several factors are usually considered in selecting an antenna for a wireless phone. Significant among these factors are the size, the bandwidth and the radiation pattern of the antenna.
The radiation pattern of an antenna is a significant factor to be considered in selecting an antenna for a wireless phone. In a typical application, a user of a wireless phone needs to be able to communicate with a satellite or a ground station that can be located in any direction from the user. Thus, the antenna connected to the user's wireless phone preferably should be able to transmit and/or receive signals from all directions. That is, the antenna preferably should have an omnidirectional radiation pattern in azimuth and wide beamwidth (preferably hemispherical) in elevation.
Another factor that must be considered in selecting an antenna for a wireless phone is the antenna's bandwidth. Generally, a wireless phone transmits and receives signals at separate frequencies. For example, a PCS phone operates over a frequency band of 1.85-1.99 GHz, thus requiring a bandwidth of 7.29%. A cellular phone operates over a frequency band of 824-894 MHz that requires a 8.14% bandwidth. Accordingly, antennas for wireless phones must be designed to meet the required bandwidth.
Currently, monopole antennas, patch antennas and helical antennas are among the various types of antennas being used in satellite phones and other wireless-type phones. These antennas, however, have several disadvantages, such as limited bandwidth and large size. Also, these antennas exhibit significant reduction in gain at lower elevation angles (for example, 10 degrees), which makes them undesirable in satellite phones.
An antenna that appears attractive in wireless phones is the dielectric resonator antenna. Until recently, dielectric resonator antennas have been widely used in microwave circuits, such as filters and oscillators. Generally, dielectric resonators are fabricated from low loss materials that have high permittivity.
Dielectric resonator antennas offer several advantages, such as small size, high radiation efficiency and simple coupling schemes to various transmission lines. Their bandwidth can be controlled over a wide range by the choice of dielectric constant (.epsilon..sub.r) and the geometric parameters of the resonator. They can also be made in low profile configurations, to make them more aesthetically pleasing than standard whip or upright antennas. A low profile antenna is also less subject to damage than an upright whip style antenna. Hence, the dielectric resonator antenna appears to have significant potential for use in mobile or fixed wireless phones for satellite or cellular communications systems.